Gradient systems are well-known for delivering a controlled mixture of two or more solvents to a liquid chromatography system.
There are two common types of gradient systems used with liquid chromatography systems. The first type is a high-pressure gradient system, which comprises two pumps operating in parallel, each pumping a solvent into a mixer at a high pressure, wherein the mixer delivers the solvent mixture to a column of a high-performance liquid chromatography (HPLC) system.
The second type is a low-pressure gradient system, which comprises a gradient proportioning valve (GPV) that mixes two or more solvents together at low pressure and outputs the resulting mixture to a single pump, which in turn delivers the solvent mixture to a sample of an HPLC system.
The GPV, however, may not provide sufficient mixing. Moreover, the volume between the GPV and the pump outlet is insufficient for mixing solvents, which can lead to compositional noise, referred to as mixing noise.
A conventional approach for reducing compositional noise is to couple a large-volume mixer to the output of the pump. However, the mixer adds undesirable delay volume to the system, which can affect the delivery of accurate and reproducible gradients as well as have a possible negative impact on cycle time for an HPLC, ultra-performance liquid chromatography (UPLC), or any liquid chromatography system. Moreover, an additional mixer may be ineffective in adequately reducing mixing noise.